<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <script src='lib/webgl-utils.js'></script>
    <script src='lib/webgl-debug.js'></script>
    <script src='lib/cuon-utils.js'></script>
    <script src="lib/cuon-matrix.js"></script>
</head>
<body onload="main()">
<canvas id="mybox" width="500" height="500">
    请更换新版浏览器查看效果!
</canvas>
<script >
    let VSHADER_SOURCE=`
    attribute vec4 a_position;
    attribute vec4 a_color;
    varying vec4 v_color;
    void main(){
    	gl_Position=a_position;
    	
    	v_color=a_color;
    }`
    let FSHADER_SOURCE=`
    precision mediump float;
    varying vec4 v_color;
    void main(){
    	gl_FragColor=v_color;
    }`


    function main(){
        let canvas=document.getElementById('mybox')
        let gl=getWebGLContext(canvas)
        if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){
            console.log('初始化shader失败');
            return;
        }
        let n=initVertexBuffers(gl)
        if(n<0){
            console.log('设置顶点位置失败')
            return;
        }
        gl.clearColor(0.0,0.0,0.0,1.0)
        gl.clear(gl.COLOR_BUFFER_BIT)
        gl.drawArrays(gl.TRIANGLES,0,n);

    }

    function initVertexBuffers(gl){
        let verticesColors=new Float32Array([0.0,0.3,1.0,0.3,0.3,  -0.3,0.0,0.0,0.5,0.5,  0.3,0.0,0.2,0.0,1.0])
        let n=3;
        let verticesColorBuffer=gl.createBuffer()
        gl.bindBuffer(gl.ARRAY_BUFFER,verticesColorBuffer)
        gl.bufferData(gl.ARRAY_BUFFER,verticesColors,gl.STATIC_DRAW);
        let FSIZE=verticesColors.BYTES_PER_ELEMENT;
        let a_position=gl.getAttribLocation(gl.program,'a_position')
        gl.vertexAttribPointer(a_position,2,gl.FLOAT,false,FSIZE*5,0)
        let a_color=gl.getAttribLocation(gl.program,'a_color')
        gl.vertexAttribPointer(a_color,3,gl.FLOAT,false,FSIZE*5,FSIZE*2)

        gl.enableVertexAttribArray(a_position)
        gl.enableVertexAttribArray(a_color)
        
        return n;
    }

</script>

</body>
</html>